AR-15 is a “genericized trademark” describing rifles that are based on a design developed by Armalite and later sold to Colt. The AR-15 was originally built as a smaller, lighter version of Armalite’s AR-10, chambered in 5.56 NATO round. The AR-10 is chambered in the larger 7.62 NATO. Armalite later sold the rights to the AR-15 design to Colt.

While there are some companies that claim to make an AR-15 style shotgun or AR-15 upper receivers chambered for a .410 shotgun shell, not only have I never actually seen one, but there has been no information to indicate the shooter had such an uncommon firearm.

Twitter was quick to ask CNN where one of these “AR-15 shotguns” could be found: